This invention relates to a data signal generation device, for use particularly, but not exclusively, as a Fieldbus signal repeater.
Fieldbus (or field bus) is the name of a family of industrial computer network protocols used for real-time distributed control, now standardized as IEC 61158. A complex automated industrial system, for example a fuel refinery, usually needs an organized hierarchy of controller systems to function. In this hierarchy there is a Human Machine Interface (HMI) at the top, where an operator can monitor or operate the system. This is typically linked to a middle layer of programmable logic controllers (PLC) via a non time critical communications system (e.g. Ethernet). At the bottom of the control chain is the fieldbus which links the PLCs to the components which actually do the work such as sensors, actuators, electric motors, console lights, switches, valves and contactors.
Fieldbus is often used in Intrinsically Safe environments, for example combustible atmospheres, and in particular gas group classification IIC, Hydrogen and Acetylene, and below, for example gas group IIB and IIA, for gas and/or dust. Using the Fieldbus protocol, field instruments and equipment in such an environment are controlled and monitored remotely via an electrical communications circuit often provided in the same electrical circuit as the power to drive the field instruments.
Fieldbus circuits are usually too large in size to support unrepeated data signals, so they comprise strategically positioned data signal repeaters to maintain the quality of the communications between the various devices. However, known Fieldbus signal repeating is usually performed by processor driven digital to analogue converters, analogue integrators, or diode clamped RC circuits. Such equipment is relatively power hungry, and it is expensive to manufacture and to purchase. With an Intrinsically Safe circuit power consumption is a critical factor in circuit design as it is always limited.
What is more, with the further development of the Fieldbus protocol in recent years, in communications and diagnostics in particular, the signal repeaters demand more and more power to perform more complex functions. Even with today's technology, the power and cost required to generate or repeat a good data signal is relatively high.
The present invention is intended to overcome some of the above problems.